In this project we use stable isotope labeling of intact plant tissues to analyze the pathways of fatty acid and lipid biosynthesis from precursors such as [13C] or [13C, 18O]acetate, [18O]water and [13C]carbon dioxide. These experiments give us information on the precursor pools, fluxes through precursor pools, and the relevance of putative hydrolytic reactions in lipid biosynthesis. Already, preliminary data for leaves suggests that the bulk acetate pool is not the primary carbon source for fatty acid synthesis and that long-chain fatty acyl export from the plastid does indeed occur via a hydrolytic mechanism. We have used MS to check the isotope composition of precursor and identification of novel natural products). More importantly, we have identified several mass spectrometry experiments which will help us unlock the fundamental question of the number of fatty acid and lipid synthesizing systems operating in the cell of the developing oilseed. These experiments will require development of mass spectrometry methods, and in particular (1) the measurement of molecular species of neutral lipids in INDIVIDUAL oil bodies, and (2) cryo-sectioning of seed tissue and mapping the 2-D distribution of lipid molecular species at as high a resolution as possible (preferably approaching resolution of a single cell), using MALDI-TOF or other focusable soft ionization technique. Both these types of experiment would expand the applicability of mass spectroscopy for the study of lipid biosynthesis and require an exciting and interactive collaboration with the MSU Mass Spectrometry Facility.